Process and apparatus for preparing lower olefins

ABSTRACT

The present invention relates to a process and apparatus for producing unsaturated hydrocarbons, particularly olefins such as ethylene by thermal cracking of hydrocarbons. In conventional tubular cracking furnaces having an external heating system, by-produced coke which accumulates on the wall of the reaction tube, transfer line and cooling tube, is a serious hindrance to operation. Therefore, it is necessary to remove the coke by a chemical means with steam or air or by a mechanical means at an interval of 60 - 90 days. Prolongation of the interval between the decoking treatments has been desired. Although countermeasures have been considered from the viewpoint of operating conditions, they cannot provide a complete solution to the problem. As for starting materials, only gaseous materials or light oil fractions permit continuous operation for as long as 60 - 90 days.

United States Patent 11 1 Ozawa'et al. Oct. 9, 1973 [5 PROCESS AND APPARATUS FOR 2,674,612 4/1954 Murphree 260/451 REP NG LOWER OLEFINS 2,513,294 7/1950 Eastwood et al. 260/683 [75] Inventors: Tokuji Ozawa, Sakai; Mikio Ueda,

Amagasaki; Ryosuke Hashimoto, Saitama; Shigenori Suzuki, Osaka,

all of Japan [73] Assignee: Mitsui Shipbuilding and Engineering Co. Ltd., Chuoku, Tokyo, Japan [22] Filed: Apr. 20, 1970 [21] Appl. No.: 30,185

[] Foreign Application Priority Data Apr. 23, 1969 Japan 44/32840 [52] U.S. Cl. 260/683 R, 208/48 R, 208/126, 23/277, 260/679 R [51] Int. Cl. C07c 11/24, C07c 3/00 [58] Field of Search 208/48, 153, 176, 208/132, 126, 127; 260/683, 679; 23/277, 284; 134/7, 87, 22 C, 165/95 [56] References Cited UNITED STATES PATENTS 2,775,546 12/1956 Kimberlin et a]. 208/126 3,573,012 3/1971 Kitzen et al 48;208/214;211 3,407,789 10/1968 Hallee et al 48/214 UX 1,939,112 12/1933 Eulberg 1 1 165/95 3,534,805 10/1970 Ackerfeldt 165/1 Evans 260/683 Primary Examiner-Delbert E. Gantz Assistant Examiner-Juanita M. Nelson Att0rneyl-lowson and Howson 57 ABSTRACT The present invention relates to a process and apparatus for producing unsaturated hydrocarbons, particularly olefins such as ethylene by thermal cracking of hydrocarbons.

' Prolongation of the interval between the decoking treatments has been desired, Although countermeasures have been considered from the viewpoint of operating conditions, they cannot provide a complete solution to the problem. As for starting materials, only gaseous materials or light oil fractions permit continuous operation for as long as 60 days.

7 Claims, 1 Drawing Figure PROCESS AND APPARATUS FOR PREPARING LOWER OLEFINS The present invention provides a process for producing olefins such as ethylene from raw materials ranging from gasoline to heavy oil fractions including crude oil in a tubular cracking furnace having an external heating system wherein by-produced coke precipitated on the wall of the apparatus is removed during the thermal cracking to make long continuous operation possible and also to increase the efficiency of the reaction, cooling and heat-recovery mechanisms, and an apparatus to be used in the process.

The process of the present invention is characterized in that solid particles such as sand are mixed and wafted in the raw materials in reaction tubes and byproduced coke precipitated and accumulated on the inner walls of the tubes is removed by collision with the moving particles. The apparatus of the present invention comprises a heating furnace including vertical tubes in which raw materials and solid particles are reciprocated to eliminate accumulation of coke on the walls cooling tubes connected with the outlets of the tubes in which the products descend, and quenchers provided with a nozzle for liquid for washing.

The present invention will be described with reference to the drawing which is diagramatical illustration of the apparatus in accordance with the present invention.

Starting hydrocarbons such as gasoline, kerosene, light oil, heavy oil or crude oil and a diluent such as steam are introduced separately or in the form of mixture in liquid or gaseous state into the lower ends of a plurality of vertical reaction tubes 3 and 3' placed in a heating furnace 2 provided with burners arranged properly. The mixture is then partially cracked by external heat while ascending in the tubes and thereafter enters dispersedly a plurality of reaction tubes and 5' via a header 4. While the mixture descends the tubes 5 and 5', it is cracked by external heat to yield olefins such as ethylene and propylene, aromatic hydrocarbons such as benzene and naphthalene and reaction products such as methane and hydrogen. Full or partial length of the ascending tubes can be used as preheater. Solid particles such as sand added for the purpose of eliminating by-produced coke precipitated and accumulated on the inner walls of the reaction tubes are supplied continuously or intermittently into a feeding system of the liquid or gaseous starting materials or into an appropriate inlet of the ascending tubes and transferred in the ascending tubes 3 and 3' in the state wafted by the stream of the starting materials, vaporous products and other gaseous materials.

Particles in the vaporous and gaseous stream which move freely are transferred into the header 4 thereby removing coke by collision with the wall, and then into the descending tubes 5 and 5' and fall in the tubes thereby removing coke in the same manner. The solid particles may also be supplied through inlets 7 and 7 at the lower portions of the reaction tubes. in the header 4, cone-shaped heat resisting structures 8 may be provided for avoiding residence of the particles in spaces between the tubes. The reaction tubes have a diameter of up to about inches and are made of heat resisting, abrasion-resisting metals. The reaction temperature is selected in the range of about 600 950C to obtain the desired treatment quantity and distribution of products. The stream of high temperature products and solid particles is thus reciprocated and reacted in the furnace and then introduced into a quenching separator 6 to check the cracking reaction and also to separate them. The quenching separator 6 includes cooling tubes 9 for cooling quickly the cracked products and a nozzle 10 for introducing oil, water or steam for dust removal and condensation of heavy oil. The high temperature stream of cracked products, diluent and particles, in contact with the cooling tubes, is heatexchanged with fluid in the cooling tubes and cooled quickly, and heat is efficiently recovered by the fluid in the cooling tubes. The solid particles also remove harmful coke accumulated on the wall of the cooling tubes. Then the cooled stream of cracked products is washed with oil, water, steam, etc. and thereby isolated from heavy oil and the particles, and sent to the next step through an outlet 11. The stream of cracked products leaving the cooling tubes is around 300C and stable. Heavy oil and the particles and oil used for washing from an outlet 12 are isolated in a known manner and recycled through a pipe 14 or used for another purpose.

As described above, according to the present invention, a long continuous operation is possible without an additional decoking operation since by-produced coke precipitated on the walls of the reaction tubes, transfer line and quenching tubes is continously removed during the cracking process. Heavy oil including crude oil which yields a large quantity of coke by-product may also be used. Further, the structure of the apparatus is efficient since the structures of the reactors and coolers are simplified.

We claim:

1. A process for thermally cracking a hydrocarbon feed stock to produce unsaturated hydrocarbons which comprises introducing ahydrocarbon feed stock into an externally heated tubular cracking furnace togeteher with a particulate abrasive material, heating said mixture to a temperature in the range from about 600 to about 950C. to convert a substantial proportion of the feed stock to gaseous unsaturated hydrocarbons and circulating the resulting fluidized, vaporous reaction mixture containing suspended abrasive particles through said tubular cracking furnace to a quenching zone, whereby deposition of by-product coke on the inner surfaces of said furnace is prevented by the scouring action of said abrasive particles.

2. A process according to claim 1 wherein the particulate abrasive material is sand.

3. A process according to claim 1 wherein the feed stock is selected from hydrocarbon fractions ranging from gasoline fractions to heavy oil fractions and crude oil.

4. An apparatus for thermally cracking a hydrocarbon feed stock comprising a plurality of reaction tubes divided into two groups for flow in opposite directions, header means providing reversal of the direction of flow in said apparatus by permitting flow out of the .inner ends of said first group of tubes into the inner to move through said apparatus carrying said abrasive material during the cracking operation so that particles thereof collide with the walls of said apparatus, whereby any carbon produced by said thermal cracking and adhering to the walls of said apparatus is dislodged therefrom by said abrasive particles.

5. An apparatus for thermally cracking a hydrocarbon feed stock comprising a plurality of reaction tubes divided into two groups for flow in opposite directions, header means providing reversal of the direction of flow in said apparatus by permitting flow out of the inner ends of said first group of tubes into the inner ends of said second group of tubes, meansfor introducing a hydrocarbon feed stock to be cracked into the outer ends of said first group of tubes, means for removing cracked hydrocarbon products from the outer ends of said second group of tubes, means for introducing particulate abrasive material to the feed stock and means for causing said feed stock and product stream to move through said apparatus carrying said abrasive material during the cracking operation so that particles thereof collide with the walls of said apparatus, whereby any carbon produced by said thermal cracking and adhering to the walls of said apparatus is dislodged therefrom by said abrasive particles, and means in said header means for preventing accumulation of said particulate abrasive material around the inner ends of said reaction tubes.

6. Apparatus according to claim 4 comprising in addition a quenching means in communication with said outlet ports of said second group of reaction tubes.

7. An apparatus for thermally cracking a hydrocarbon feed stock comprising a plurality of reaction tubes divided into two groups for flow in opposite directions, header means providing reversal of the direction of flow in said apparatus by permitting flow out of the inner ends of said first group of tubes into the inner ends of said second group of tubes, means for introducing a hydrocarbon feed stock to be cracked into the outer ends of said first group of tubes, means for removing cracked hydrocarbon products from the outer ends of said second group of tubes, means for introducing particulate abrasive material to the feed stock and means for causing said feed stock and product stream to move through said apparatus carrying said abrasive material during the cracking operation so that particles thereof collide with the walls of said apparatus, whereby any carbon produced by said thermal cracking and adhering to the walls of said apparatus is dislodged therefrom by said abrasive particles, a quenching means in communication with said outlet ports of said second group of reaction tubes, and means in said header means for preventing accumulation of particulate abrasive material around the inner ends of said reaction tubes. 

2. A process according to claim 1 wherein the particulate abrasive material is sand.
 3. A process according to claim 1 wherein the feed stock is selected from hydrocarbon fractions ranging from gasoline fractions to heavy oil fractions and cruDe oil.
 4. An apparatus for thermally cracking a hydrocarbon feed stock comprising a plurality of reaction tubes divided into two groups for flow in opposite directions, header means providing reversal of the direction of flow in said apparatus by permitting flow out of the inner ends of said first group of tubes into the inner ends of said second group of tubes, means for introducing a hydrocarbon feed stock to be cracked into the outer ends of said first group of tubes, means for removing cracked hydrocarbon products from the outer ends of said second group of tubes, means for introducing particulate abrasive material to the feed stock and means for causing said feed stock and product stream to move through said apparatus carrying said abrasive material during the cracking operation so that particles thereof collide with the walls of said apparatus, whereby any carbon produced by said thermal cracking and adhering to the walls of said apparatus is dislodged therefrom by said abrasive particles.
 5. An apparatus for thermally cracking a hydrocarbon feed stock comprising a plurality of reaction tubes divided into two groups for flow in opposite directions, header means providing reversal of the direction of flow in said apparatus by permitting flow out of the inner ends of said first group of tubes into the inner ends of said second group of tubes, means for introducing a hydrocarbon feed stock to be cracked into the outer ends of said first group of tubes, means for removing cracked hydrocarbon products from the outer ends of said second group of tubes, means for introducing particulate abrasive material to the feed stock and means for causing said feed stock and product stream to move through said apparatus carrying said abrasive material during the cracking operation so that particles thereof collide with the walls of said apparatus, whereby any carbon produced by said thermal cracking and adhering to the walls of said apparatus is dislodged therefrom by said abrasive particles, and means in said header means for preventing accumulation of said particulate abrasive material around the inner ends of said reaction tubes.
 6. Apparatus according to claim 4 comprising in addition a quenching means in communication with said outlet ports of said second group of reaction tubes.
 7. An apparatus for thermally cracking a hydrocarbon feed stock comprising a plurality of reaction tubes divided into two groups for flow in opposite directions, header means providing reversal of the direction of flow in said apparatus by permitting flow out of the inner ends of said first group of tubes into the inner ends of said second group of tubes, means for introducing a hydrocarbon feed stock to be cracked into the outer ends of said first group of tubes, means for removing cracked hydrocarbon products from the outer ends of said second group of tubes, means for introducing particulate abrasive material to the feed stock and means for causing said feed stock and product stream to move through said apparatus carrying said abrasive material during the cracking operation so that particles thereof collide with the walls of said apparatus, whereby any carbon produced by said thermal cracking and adhering to the walls of said apparatus is dislodged therefrom by said abrasive particles, a quenching means in communication with said outlet ports of said second group of reaction tubes, and means in said header means for preventing accumulation of particulate abrasive material around the inner ends of said reaction tubes. 